1. Field of the Invention
The invention relates in general to an uninterruptible power supply (UPS), and more particularly to a power saving UPS that has low power consumption.
2. Description of the Related Art
In general, UPS has three types, a first one is on-line UPS, a second one is off UPS and a third one is line interactive UPS. With reference to FIG. 3, an improved on-line UPS 60 is disclosed by U.S. Pat. No. 5,229,650 and has a rectifier 61, an inverter 62, a charger 63, a battery 631 and a control signal generator 64. The rectifier 61 is coupled to a utility power and inputs of the inverter 62. The charger 63 is connected to the battery 631 and the utility power through a first switch SW1. The battery 631 is connected to the inputs of the inverter 62 through a second switch SW2. The control signal generator 64 is connected to the utility power, the battery 631 and the first and second switches SW1, SW2 to drive the first and second switches SW1, SW2. Outputs of the inverter 62 are connected to a load 65.
When the utility power is stable, the rectifier 61 converts the utility power to a DC power source and then outputs the DC power source to the inputs of the inverter 62. The inverter 62 converts the DC power source to the AC power source for the load 65. At the time, the control signal generator 64 detects that utility power is stable and further determines whether electricity of the battery 631 is full or not. If determining result is positive, the first switch SW1 is driven to open by the control signal generator 64. If not, the control signal generator 64 drives to the first switch SW1 to close. The utility power outputs to the charger 63 and then the charger 63 charges to the battery 631.
When the control signal generator 64 detects that the utility power is unstable or interrupted, the control signal generator 64 drives the first switch SW1 to open and the second switch SW2 to close. Another DC power source from the battery 631 is supplied to the inputs of the inverter 62. The inverter 62 converts the DC power source to the AC power source for the load 65. Therefore, the load 65 can still operate normally even the utility power is unstable or interrupted. Since the on-line UPS 60 has the control signal generator 64 and the first switch SW1, the battery 631 is not continuously charged by the charger 63, so the battery life can be increased.
In general, the line-interactive UPS further requires a voltage regulation transformer (hereinafter AVR) to stable the unstable utility power. The DC power source of the battery is only supplied to the inverter at a condition that the utility power is interrupted. Therefore, the line-interactive UPS provides the stable AC power source to the load. However, the AVR has a huge size, low transforming efficiency etc. drawbacks. Therefore, US 2004/0036361 patent proposes an improved line-interactive UPS. With reference to FIG. 4, the line-interactive UPS 70 has a bi-directional AC to AC power converter 71, a first switching unit 72, a second switch 73 and a third switch 74. The first switching unit 72 has two switches SWA respectively connected to a line terminal A and a neutral terminal B of the AC to AC power converter 71. Common nodes of the second and third switches 73, 74 are respectively connected to a load 75. Two switching nodes of the second switch 73 are respectively connected to the line terminal A and a line output terminal B of the AC to AC power converter 71. Two switching nodes of the third switch 74 are connected to the line terminal A and the neutral terminal B of the AC to AC power converter 71. When the utility power is stable, the first switching unit 72 is closed and the load 75 is connected to the line terminal A and the neutral terminal B of the AC to AC power converter 71. Therefore, the utility power is supplied to the load 75 directly. When line voltage of the utility power exceeds a high standard value, only the second switch 73 is switched to connect the neutral output terminal C of the AC to AC power converter 71. When the utility power is interrupted, the second switch 73 is switched to connect the neutral output terminal B of the AC to AC power converter 71 and the third switch 74 is switched to connect the line terminal A of the AC to AC power converter 71. Since the AC to AC power converter 71 does not uses a transformer, the size of the line-interactive UPS is decreased and the transforming efficiency is increased.
The above line-interactive UPS does not require the AVR and the line-interactive UPS also does not other advantages of the AVR.